Chromatography is a chemical separation technique utilizing the fact that substances to be separated are distributed in different ways between a stationary phase and a mobile phase. In liquid chromatography, the mobile phase is a liquid. The stationary phase, or separation medium, which typically is an adsorption medium, an ion-exchanger material, a gel or a surface-modified solid material, is usually packed in a column. Different components in a sample applied to the top of the medium bed will migrate through the column at different rates depending, e.g., on their size and degree of attraction to the stationary phase when the liquid passes through the column. Liquid chromatography is extensively used for chemical analysis as well as for preparative separations in research and industry.
In traditional chromatography, the liquid or solvent passes through the column by gravity. The rate at which the liquid passes through the column is therefore relatively slow. To speed up the rate of the chromatography process, the liquid is forced through the column by the application of a positive pressure. This may be accomplished by pumping the liquid through the column, such as in HPLC (high performance liquid chromatography), or by the application of a positive air-pressure, such as in traditional flash chromatography.
Flash chromatography is a rapid form of preparative column chromatography which dates back to 1978 (W. C. still et al., J. Org. Chem. 1978, 43, 2923-2925) and uses pre-packed disposable columns or cartridges, typically of plastic. In modern flash chromatography variants, the liquid is pumped through the column or cartridge.
The disposable columns used for flash chromatography are usually manufactured with economy in mind, which involves manufacturing the columns of inexpensive plastics and designing the columns to be easily assembled by filling the body of the column with the desired packing, usually with frit plugs on each end of the packing to hold the packing in place, and then closing the open end or ends of the columns by end pieces or caps, e.g. by screwing or snapping them to the column ends, or, more typically, attaching them by spin welding or heat plate welding.
Various column designs have been devised to improve the pressure stability and cost-efficiency in producing the columns or cartridges.
US 2003-0102266 A1 discloses a flash chromatography column assembly comprising a single-ended cartridge containing a chromatographic sorbent, and a compression head configured to cover the upper end of the cartridge and to compress the sorbent within the interior volume of the cartridge. The compression head includes a disk-shaped cover dimensioned to fit within and seal the upper end of the cartridge and a structure for transmitting a compression force to the cover to compress the sorbent in the interior volume.
WO 2007/005508 discloses a single-use chromatography column having an end plate that is fixed to the column end by spin welding. To this end, the end plate includes radially extending ridges that permit gripping by conventional spin welding equipment to spin the end plate for the purpose of a spin weld. The spin welded seal is intended to maintain its seal under higher pressures.
U.S. Pat. Nos. 6,177,328 and 6,398,953 disclose a method of supporting a media bed in a chromatography cartridge tube wherein an end cap is cooled to thermally contract the end cap to a dimension less than the inner diameter of the tube. The contracted end cap is then placed within the tube and against the media bed, and the end cap is sealed to the tube by thermal expansion of the end cap upon warming. The expansion of the end cap causes the tube to deform locally to secure the end cap within the tube.
US 2005/0161382 A1 discloses a method of forming a column for use with an analytical chemical instrument. The method comprises placing a fit in proximity of a distal end of a tube with an internal bore adapted to receive a packing material, laser welding the fit to the tube, and inserting a packing material within the internal bore of the tube. The frit is formed from a porous material, and laser welding the frit substantially reduces the volume of the porous material to leave a porous passageway through the frit.
US 2005/022414 A1 discloses a chromatography column having an inlet filter assembly which is securely fixed to the column tube by welding, heat sealing or glueing.
The prior art flash chromatography columns or cartridges, however, still have deficiencies including, for example, problems with dead volumes, insufficient pressure stability, spin welding causing melting of plastic frits, and production effectiveness.
There is therefore a need for improvements in the design of disposable plastic columns or cartridges, and especially to provide columns or cartridges which are pressure stable and can be produced in a cost-efficient way.